EP0026413A1 - Circuit arrangement for registering the switching state in a circuit especially constituted by subscriber lines in telephone exchanges - Google Patents

Abstract

The switching state of a subscriber line (open or closed loop) is registered by a comparator (K). One input of this comparator is coupled to a line point, which characterizes the respective switching state on the basis of the potential states occurring at it (connection point of the supply resistance, which is turned away from the supply voltage source). The other input receives a reference voltage that defines a threshold separating the two measuring ranges. For a plurality of lines, the respective effective connection takes place via a correspondingly controlled selector (S) in a predetermined cycle. The output signal of the comparator is delayed by the cycle time (shift register SR), supplied to further processing units (ZST) and, on the other hand, individually superimposed on the specified comparison value for the subsequent voltage evaluation relating to one and the same measuring point in the cycle. This prevents a change in the output signal when there is a change in the measured value within a fluctuation range caused by interference.

Description

The invention relates to a circuit arrangement for deriving a control signal in cases in which a DC voltage measured value which arises due to a switching measure to be registered at a measuring point from a plurality of similar measuring points in a respective switching circuit passes through a predetermined reference voltage value separating two possible measuring ranges, the individual Measuring points are switched through cyclically one after the other by an electronic selector circuit to the one input of a comparator, which enables this registration by outputting an output signal that differs from one another depending on the direction of passage, to the other input of which the reference voltage value is supplied, in particular for Assessment of the operating state of subscriber lines in telephone switching systems, each of which forms one of the switching circuits mentioned, including the office-side supply circuit and the call station.

It is assumed that there is an arrangement in which the voltage states of individual measuring points can be determined one after the other by means of a selector circuit, which is periodically recurrently activated by a comparator. Such a comparator is therefore jointly available for a number of measuring points corresponding to the number of selector steps. If the number of measuring points goes beyond this, these can be queried in the same way by one or more further selector circuits, which are each effective again after a certain cycle time.

A comparative voltage value is specified for the comparator, by which a threshold is determined. In this way, for example, two measuring ranges to be assigned to the possible switching states in a circuit can be separated. As long as the measured value available at the respective time of inquiry within each measuring range clearly differs from the predetermined threshold value, it is possible to assign the respective output signal of the comparator to one of these ranges without problems. However, if the measured value is in the immediate vicinity of the predefined threshold value, it must be ensured that a clear statement is made, in particular in the case of slight changes in the measured value, which can be caused, for example, by interference. This means that there is a slight fluctuation around the threshold up or down should not lead to a change in the output signal. The transition of the measured value from one measuring range to the other measuring range between two successive measuring times can be defined by a voltage jump in the output voltage of the comparator. For a comparator that is used to compare two voltage values, it is known per se to achieve hysteresis behavior by means of an additional positive feedback in the plus input.

The circuit formed via the supply voltage source, the subscriber line loop and the intercom station can be considered as the switching circuit, the switching state of which is to be assessed. If a supply via corresponding supply resistances, which are inserted into each of the two wires and connected to the central supply voltage source, is provided for each microphone unit within the subscriber connection circuit assigned to it at the office, the connection point of the supply resistance, for example, which is not directly connected to the positive pole of the supply voltage, can be used as the measuring point be used.

It is the object of the invention to enable a clear assignment of the respective measuring range to the output signal of the comparator in the arrangement of the type mentioned at the beginning when a limit case described above occurs. This is achieved in that the output signal of the comparator resulting for each measuring point is only transmitted as a control signal to further control units for further processing after a delay time corresponding to the cycle time individually for the subsequent voltage evaluation relating to one and the same measuring point in the cycle, the fixed predetermined comparison voltage value is superimposed via a decoupling adaptation element in such a way that a change in the triggered control signal in the event of measurement value changes within a predetermined fluctuation range related to the reference voltage value and caused by interference is excluded.

According to the invention, the result of a query of the respective measuring point is therefore not output immediately, but rather delayed by the cycle time and, for example, transferred to a central control device as a downstream device for further processing. At the same time, depending on the output signal of the comparator determined in the previous query of one and the same measuring point, which corresponds to a certain logic potential, a change in the relevant comparison voltage value may be effected for the pending evaluation. For this purpose, the output signal to be assigned to the previous query of the same measuring point is superimposed in a corresponding manner on the comparison voltage. This is possible with the connection made by the selector circuit for a predetermined number of measuring points in correct time assignment. A dynamic change range must therefore be provided individually for each measuring point. Because of the slight shift in the comparison voltage in that direction, which would lead to a response characterizing the other measured value range, the comparator can only then assume an initial state assigned to this range if the value of the voltage to be measured has changed in value by more than the shift made.

According to a development of the invention, in order to delay the output signal of the comparator, this is input into a respective shift register, the shift clock of which is derived directly from the respective control act for the selector circuit. The number of shift steps of this shift register corresponds to the number of measuring points queried by the selector circuit.

In particular when polling subscriber lines, such a shift register is necessary anyway to adapt to the time relationships on which the work processes are based. It must namely be ensured that only the information corresponding to a steady state of the relevant components or units is evaluated. There is therefore multiple use of this shift register.

According to a further development of the invention, the comparison voltage value is specified via a fixed divider arrangement and a shift of the comparison voltage value is effected depending on the output information of the shift register relating to the previous query. According to the invention, a correspondingly wired integrated differential amplifier, preferably an operational amplifier, is used as the comparator.

• FIG 1 zeigt den grundsätzlichen Schaltungsaufbau für die Bewertung der Potentialverhältnisse an einem Messpunkt.
• FIG 2 zeigt eine grafische Darstellung zur Erläuterung der Veränderung des Ansprechwertes.

The invention is explained in more detail below with reference to the figures.

• 1 shows the basic circuit structure for evaluating the potential relationships at a measuring point.
• 2 shows a graphic representation to explain the change in the response value.

1 shows only the components or structural units necessary for understanding the invention. The selector circuit S should serve to query the potential states at the individual measuring points. This selector circuit can be a commercially available integrated multiplexor. It can be used to query a number of measuring points corresponding to the number of its inputs E1 to En, each of which is coupled to one of these inputs. The information at the respective inputs is then switched through to the output. For the individual input, this is done by applying, for example, a binary-coded address to the address inputs A of the selector circuit. This can be done either in any order or in such a way that the individual inputs are selected in immediate succession by means of a corresponding, continuous addressing for switching the input information to the output. In the exemplary embodiment, a circuit point that characterizes the potential state of a subscriber line is used as the measuring point. The subscriber line Ltg leading to the subscriber station Tnl is connected via the windings W1 and W2, respectively, of a fork transformer U, which are inserted into the respective wires a and b, to the feed circuit, which forms part of the subscriber line circuit available for each subscriber on the office side. The supply circuit consists of the two supply resistors R1 and R2. The resistance R1 is in the earth potential horizontal wire, the b-wire, and the resistor R2 inserted in the am.potential potential, the a-wire of the subscriber line. Capacitor C bridges the two line wires at the terminals of the two resistors facing away from the supply source. The secondary-side windings of the transmitter U, which decouples, among other things, the direct current paths of the calling and the called subscriber station, is not shown further. The other components of the subscriber line circuit, such as the switching means for call connection, are also not shown.

Depending on the operating state of the subscriber line, different potential relationships now occur on the supply resistors, for example on the supply resistor R1. As a result, the lifting of the handset, dialing pulses and other switching indicators as a result of their voltage drop across the resistor R1 can be determined by a corresponding voltage evaluation. When the subscriber loop is open, potentials arise on the line wires, which are determined by the size of the supply voltage -UB and the leakage resistances of the line. The potential on the a wire is approximately equal to the supply voltage -UB and that of the b wire is almost zero. If the loop is closed, the voltage difference between the wires drops to a small value dependent on the loop resistance, while the potential at the feed resistor R1 changes to a voltage drop determined by the resistance value and the loop current. The operating state of the subscriber line can therefore be registered by a corresponding measurement of the voltage drop across resistor R1. This is one of the inputs E1 to En of the selector are connected indirectly to the line wire via a voltage divider formed from resistors R3 and R4. The voltage divider brings the voltage drop that occurs at the resistor R1 when the loop closes to a voltage value that can be switched through by means of the integrated selector circuit S. A commercially available, integrated selector circuit can be used to query a group of n, for example 16, subscriber lines via the corresponding number of inputs. For this purpose, these inputs are then individually connected to a divider point of the divider circuit available for each subscriber line.

If the operating state of more than n _- in the same way be scanned lines so are to be grouped via respective selector circuits further line groups. The input voltage present at an input E and defining the switching state of a subscriber line is switched through to the output by the address information when the corresponding input is selected and fed to the inverting input of an integrated comparator K. At the positive input of this comparator there is a comparison voltage which is derived from the supply voltage by the divider circuit consisting of the resistors R5 to R7. When assessing the switching status of subscriber lines, this reference voltage value is set so that, with the permissible leakage resistances and the existing scatter in the line resistance, it is possible to clearly separate the areas assigned to the open and closed state of the subscriber line loop. It is conceivable to additionally supply the positive input of the comparator with a voltage which arises at the connection point of two high-resistance resistors, that form a cross-branch between the cable cores. As a result, couplings of interference components of a certain order of magnitude caused by a power line can no longer have a disadvantageous effect. These then coincide at the coupling points and thus at the two inputs of the comparator K with respect to the amount, the phase and the frequency, so that they are eliminated in the difference formation carried out by the comparator. This further voltage can then be supplied to the input of the comparator in the same way as is done for the inverting input by a further selector circuit of the same type.

Depending on whether the measuring voltage supplied to the inverting input via the selector circuit at the respective query time is above or below the predetermined comparison voltage, an output signal of the comparator which is clearly different from one another arises. This respective output signal should then correspond to logic potential zero or logic potential one. When polling subscriber lines, for example, the output signal that results from a closed line loop should correspond to logic potential 1. In this case, the measured voltage value supplied to the comparative test is above the set reference voltage value. The output signal of the comparator is input into a downstream shift register SR, which has a number of steps corresponding to the number of measuring points to be queried via a selector circuit S. After the query of each measuring point within the group of n measuring points in each case, the shift register is advanced via a corresponding clock pulse. That beat Like the address information for the selection of one of the inputs E1 to En, impulse can be triggered by a central control device ZST in the event of a query of subscriber lines. Assuming that further groups of measuring points are combined in the same way via other selector circuits, the query of the nth subscriber line follows in the same way the query of the other groups in the order determined by the central control device. After the scheduled cycle time has elapsed, the same measuring point or the subscriber line assigned to this measuring point in the exemplary embodiment is queried again. Each time after the scheduled cycle time has elapsed, for example, the selector circuit S is reactivated and the individual inputs are switched on to the one input of the comparator in succession by means of corresponding address information from the central control device. This means that the output signal relating to one and the same measuring point appears at the output of the shift register with a cycle time delay. This output signal is then communicated to the central control device via an interface St, which converts the respective information in the same way as other information supplied to it into corresponding logic potentials zero and one. This then initiates the procedures resulting from the respective output signal. The control information that is occasionally provided by this central control device for controlling the individual address inputs and for switching the shift register forward is effectively passed on via the respectively assigned interface St.

The output signal of the shift register SR continues out through an isolation amplifier T and a resistor R8 to the connection point of the two resistors R6 and R7. These resistors form a partial resistance of the divider circuit which supplies the comparison voltage. In this way, the respective effective threshold value is influenced as a function of the result of the immediately preceding query of the same measurement point. This is because the status corresponding to the previous query is output at each output of the shift register and, if necessary, the reference value for the response of the comparator K is changed by a corresponding voltage superimposition. This change occurs in such a way that the response threshold is shifted slightly in the direction of a positive feedback in the direction that would result in a contrary statement in the output signal of the comparator if the measured value were exceeded. It is thereby achieved that with a measured value voltage which is in the immediate vicinity of the predetermined response threshold, there is no change in the output signal of the comparator with slight changes in the measured voltage, for example due to interference. This is only the case if a change occurs for the measured value voltage that is greater than the shift in the response threshold made at the time of measurement. When polling subscriber lines, it is ensured, for example, that no oscillating statements are made in the output signal of the comparator in the cases in which leakage resistances occur which result in a voltage value approximately corresponding to the predetermined threshold value. This then applies in each case to a change in the measured value voltage in the range defined by the adjustment of the relevant threshold value becomes. Changes that go beyond this result in a change in the output signal.

This mode of operation is illustrated by the diagram in FIG. 2. The curves U1, U2 prescribe voltage profiles which enable the comparator to make a clear statement since they clearly differ from the response value. A clear statement is given at each sampling time ta. In the case of line monitoring, the voltage values corresponding to curve U1 should correspond, for example, to the values occurring in the case of a closed line loop. This should then result, for example, in an output signal from the comparator K which corresponds to the logic potential 1. The measured values corresponding to curve U2 for the respective sampling points ta should result from an open line loop at the measuring resistor. This results in an output signal of the comparator which is opposite to the measurement points in accordance with curve U1. By definition, this output signal should then correspond to the logic potential zero.

Curve U3 shows a voltage curve for the measured value, which should be in the immediate vicinity of the response value Us, which is predetermined for the comparator by the divider circuit consisting of resistors R5 to R7. If this value were to change due to interference, such that its absolute value for one sampling time ta1 is above this response value, for example, and for the immediately following sampling time ta2 is below the response value, this would result in conflicting statements in the comparator output signal. Now this will be This prevents the response threshold for the subsequent query from being automatically shifted depending on the result of the previous query. Assuming that an output signal corresponding to logic potential one has resulted for the sampling time ta1, the threshold voltage for a subsequent query will now be around a certain range Uh after the cycle time, which corresponds to the difference between the two query times ta2 and ta1 lowered so that the threshold voltage Usu results in the assumed example. At the time of measurement ta2 there is no change in the output signal of the comparator. In the same way, this should be the case for subsequent measurement times. This change, ie the jump to the opposite switching state, should only occur at the sampling time ta4, since the measured value falls below the reduced threshold value. The change in the output signal of the comparator means that the threshold is raised again by the range Uh for the subsequent query time ta5. If this threshold, which is decisive for this sampling time, is not exceeded by the measured value, then this threshold value is retained for the subsequent sampling times. If the measured value voltage exceeds this threshold value again, there is a change in the output signal. The measured value has thus changed by an amount that exceeds the amount Uh defining a fault range. As a rule, this will not be caused by interference, but it will be the result of a change in the switching state of a polled subscriber line. This change in the switching state is then correctly signaled by a change in the output signal of the comparator.

Claims (4)

1.Circuit arrangement for deriving a control signal in cases in which a DC voltage measured value which arises due to a switching measure to be registered at a measuring point from a plurality of similar measuring points in a switching circuit in each case passes through a predetermined comparison voltage value separating two measuring ranges, the individual measuring points being cyclically in succession are switched through by an electronic selector circuit at one input of a comparator, which enables this registration by outputting an output signal which differs from one another depending on the direction of passage, to the other input of which the reference voltage value is supplied, in particular for evaluating the operating state of subscriber lines in telephone exchanges including one of the switching circuits mentioned, including the office-side supply circuit and the intercom, dadu rch characterized that the resulting output signal of the comparator (K) is only transmitted after a delay time corresponding to the cycle time as a control signal for further processing to downstream control units (ZST) as well as individually for the same measuring point in the cycle The subsequent voltage evaluation in question is superimposed on the fixed predetermined comparison voltage value via a decoupling adapter (T) in such a way that a change in the triggered control signal in the event of changes in measured values within a predetermined fluctuation range based on the comparison voltage value and caused by interference is excluded. 2. Circuit arrangement according to claim 1, characterized in that, for delay, the comparator output information is entered in each case into a downstream shift register (SR), the shift clock of which is derived directly from the respective control clock of the selector circuit and the number of shift steps corresponds to the number of queried measuring points. 3. Circuit arrangement according to claim 1, characterized in that the comparison voltage value is predetermined via a fixed divider arrangement (R5 to R7) and that, depending on the output information relating to the previous query of the shift register, a shift of the comparison voltage value is made possible at the time of the immediately subsequent query. 4. Circuit arrangement according to one of the preceding claims, characterized in that an appropriately wired integrated differential amplifier is used as the comparator.

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